The present invention relates to containers for dispensing liquids, particularly refill containers for dispensing inks or solvents for use in printers, such as ink jet printers, particularly continuous ink jet printers. The invention also relates to methods for monitoring the amount of liquid remaining in such containers and to an ink jet printer connectable to a container of the kind referred to above.
In ink jet printing systems, the print is made up of individual droplets of ink generated at a nozzle and propelled towards a substrate. There are two principal systems: drop on demand where ink droplets for printing are generated as and when required; and continuous ink jet printing in which droplets are continuously produced and only selected ones are directed towards the substrate, the others being recirculated to an ink supply.
Continuous ink jet printers supply pressurised ink to a print head drop generator where a continuous stream of ink emanating from a nozzle is broken up into individual regular drops by an oscillating piezoelectric element. The drops are directed past a charge electrode where they are selectively and separately given a predetermined charge before passing through a transverse electric field provided across a pair of deflection plates. Each charged drop is deflected by the field by an amount that is dependent on its charge magnitude before impinging on the substrate whereas the uncharged drops proceed without deflection and are collected at a gutter from where they are recirculated to the ink supply for reuse. The charged drops bypass the gutter and hit the substrate at a position determined by the charge on the drop and the position of the substrate relative to the print head.
Typically, the substrate is moved relative to the print head in one direction and the drops are deflected in a direction generally perpendicular thereto, although the deflection plates may be oriented at an inclination to the perpendicular to compensate for the speed of the substrate (the movement of the substrate relative to the print head between drops arriving means that a line of drops would otherwise not quite extend perpendicularly to the direction of movement of the substrate).
In continuous ink jet printing a character is printed from a matrix comprising a regular array of potential drop positions. Each matrix comprises a plurality of columns (strokes), each being defined by a line comprising a plurality of potential drop positions (e.g. seven) determined by the charge applied to the drops. Thus each usable drop is charged according to its intended position in the stroke. If a particular drop is not to be used then the drop is not charged and it is captured at the gutter for recirculation. This cycle repeats for all strokes in a matrix and then starts again for the next character matrix.
Ink is delivered, under pressure, to the print head by an ink supply system that is generally housed within a sealed compartment of a cabinet that includes a separate compartment for control circuitry and a user interface panel. The system includes a main pump that draws the ink from a reservoir or tank via a filter and delivers it under pressure to the print head. As ink is consumed the reservoir is refilled as necessary from a replaceable ink cartridge that is releasably connected to the reservoir by a supply conduit, with the replacement ink suitably being supplied through an ink top-up pump which is connected to an outlet port of the replaceable ink cartridge by means of the supply conduit. The ink is fed from the reservoir, suitably via a flexible delivery conduit to the print head by the main pump. The unused ink drops captured by the gutter are recirculated to the reservoir via a return conduit by a pump. The flow of ink in each of the conduits is generally controlled by solenoid valves and/or other like components.
As the ink circulates through the system, there is a tendency for it to thicken as a result of solvent evaporation, particularly in relation to the recirculated ink that has been exposed to air in its passage between the nozzle and the gutter. In order to compensate for this “make-up” solvent is added to the ink as required from a replaceable solvent cartridge so as to maintain the ink viscosity within desired limits. This solvent may also be used for flushing components of the print head, such as the nozzle and the gutter, in a cleaning cycle. A solvent top-up pump may be used for supplying the solvent from the replaceable solvent cartridge via a supply conduit.
Hence a typical continuous ink jet printer has both a replaceable ink container, or cartridge and a replaceable solvent container, or cartridge. Suitably, each container has a port through which the respective liquid, ink or solvent, is dispensed. The port for each container is connected, via fluid-tight means, to a pumping system adapted to dispense liquid from the container to the reservoir. In this description, both replaceable ink containers and replaceable solvent containers are referred to as containers or cartridges.
It is desirable to provide a simple method for monitoring the quantity of ink or solvent remaining in a container for a printer. This is because such monitoring allows for an operator of the printer to plan for replacement of the container at a suitable time, such as when the printer is not in use, without disrupting the printer's operation.
Also, it may be desirable to change the ink type or solvent type for a printer before the ink or solvent containers are empty (for instance because a different ink colour or type is needed). It is desirable to be able to re-attach such part-used containers at a later date so that ink or solvent is not wasted. It is also desirable to be able to know the amount of liquid remaining in part-used containers when they are to be re-used, either with the printer from which they were removed when partially full, or with another compatible printer.